I would take a guess that you don't have sendmail set up right. (trust me, I racked my head for DAYS!! DAYS I SAY!! trying to figure this out)
No, you don't have to fuck with MX records or BIND. As long as sendmail is set up right, when an e-mail gets sent to your web address, it will come to your IP, (through dyndns) (really, all dyndns does, is listen for a request for logan5.com, and when they get a request, their name servers, point that request to your IP. )
If you have sendmail installed, look at sendmail.cf & sendmail.mc
(note: you may have to install the sendmail.cf package, this enables you to "re-build" the sendmail config file.)
In one of the above files, look for a line...shit *is thinking and scratching head*
Um.. there is a line in there that makes sendmail listen only on localhost. or 127.1.1.0 or whatever, anyway, UN-COMMENT that line, then save the file, rebuild sendmail.cf and restart sendmail.
I have to set it up on another machine this weekend so I could give ya a more descriptive help then... ( i just finished an 11 hour work day)
hope that helps











